Frustrated lewis pair
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An excellent utilisation of frustrated energy between sterically crowded lewis pairs for the development of a metal free alternative method for catalytic hydrogenation.
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Lithium is a soft, silvery metal that is the lightest of all metals and the first element in the alkali metal family, having an atomic number of 3. As the least dense of all metals, lithium has a low melting point of 180 degrees Celsius and is very reactive, especially with water. Lithium and its compounds have various industrial and medical uses such as in lithium-ion batteries, psychiatric medications, and air treatment to remove carbon dioxide from the air.
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Frustrated lewis pair
- 1. Frustrated Lewis Pairs M. K. Sahoo
- 2. B F F F N H H H N H H H BF F F Lewis Acid (Electron Pair Acceptor) Lewis Base (Electron Pair Donor) Lewis Acid-Base Adduct G. N. Lewis, FRS, 1923: Valence & Structure of Atoms & Molecules Lewis Acid Base Concept
- 3. Frustrated Lewis Pairs (FLP) Combination of sterically hindered Lewis donors and lewis acceptors B P
- 4. • 1923 : Lewis • Lewis Base : an electron pair donor • Lewis Acid : an electron pair acceptor • 1942 : Brown • 1959 : Wittig and Benz • Ancestor of the Frustrated Lewis Pair • 1966 : Tochtermann • « Antagonistisches Paar » F Br Mg PPh3 BPh3 PPh3 BPh3 BF3 BM e3 No ReactionNN BF3 CPh3Na BPh3 Ph3C BPh3 NanNa Ph3BCPh3 CPh3Na BPh3 Historical Background
- 5. Prof D. W. Stephan: Father of FLP First non-transition metal system that can reversibly activate & liberate hydrogen
- 6. 1. Creation of a polar and frustrated environment BR3R3P H H 2. Polarization of H2 3. Activation of H2 Why would an FLP activate H2? Facts on H2 bond 0.74 Å 432 kJ/mol
- 8. Mechanism of H2 Activation by FLPs 1. 2.
- 10. Grimme et.al.; Angew. Chem. Int. Ed. 2010, 49, 1402 Electric Field Model
- 12. Papai et.al; J. Am. Chem. Soc. 2013, 135, 4425-4437 Electric Field along H-H Axis For six FLPs
- 14. Phosphines Carbenes Imines Amines Boranes Linked Frustrated Lewis Pairs Non-Linked Frustrated Lewis Pairs
- 15. Sufficient Acidity & Basicity is key for Activation Factors Responsible for Activation 3
- 16. Decreased Lewis Acidity & Basicity Allow Reversible Activation (C6H5)3B (o-C6H4Me)3P(p-C6F4H)3B Reversible Activation
- 17. 2,6-Lutidine exibhits Classical and FLP behaviour Dialkylethers, THF, Dioxane also shows dual behaviour Classical Vs FLP: Orthogonal???
- 18. Hydrogenation: Additon of molecular hydrogen (H2) to another molecule Cleanest Reducing Agent, 100% Atom Economy Food, Petrochemicals, Agricultural, Pharmaceutical Industries X Y H 2 X Y H H Application: Catalytic Hydrogenation
- 19. HYDROGENATION HISTORY Paul Sabatier, 1897, trace nickel (as a catalyst) to facilitate addition of H2 to organic compounds. (Nobel Prize 1912) Sir Geoffrey Wilkinson FRS, 1966, “one of the fathers of organometallic Chemistry” discovered homogeneous Rh catalyst for hydrogenation (Nobel Prize 1973) Ryōji Noyori FRS,1994, introduction Ru catalyst for Highly selective asymmetric hydrogenations (Nobel Prize 2001)
- 21. ( Current Technologies) Transition metal free Hydrogenation
- 22. 1. Catalytic Hydrogenation of Imines X Y H2 XY HH FLP FLP[H...H]
- 23. Mechanism of Catalytic reduction
- 24. Catalytic Reduction: B(C6F5)3 Protected Imines
- 25. 2. Imines as Basic FLP Partner Ph2C
- 26. Mechanism
- 27. 3. Hydrogenation of Nitriles
- 28. 4. Hydrogenation Of N-Heterocycles
- 29. 5. Hydrogenation of Carbonyl Compounds R R' O R R' OHCat:B(C6F5)35-20mol%, H2(5Bar) T(80-1000C),t(06-120hrs) Dioxane 99% 60% 0% 99% 80% 14% 84% 99% 97% 82% 78% 0% 75% O B(C6F5)3 O B(C6F5)3 ClassicalFLP H2 O H n H-B(C6F5)3
- 30. Mechanism Ashley et. al.; J. Am. Chem. Soc. 2014, 136, 15813-15816 A. nBu4N H-B(C6F5)3 Ketone No Reaction nBu4N H-B(C6F5)3 Ketone Sec Alcohol B(C6F5)3 nBu4N H-B(C6F5)3 Aldehyde Primary Alcohol B. OH n H-B(C6F5)3
- 31. 6. Hydrogenation by FLPs (other functional Groups) FLP Silylenolethers
- 32. P C6H6 C6F5C6H6 P C6H6 C6F5C6F5 P C6H3Cl2 C6H3Cl2Cl2C6H3 P 1-Napthyl 1-NapthylNapthyl-1 7. Hydrogenation of Nonpolar Substrates (Alkenes)
- 33. Olefin Nucleophilicity (N): 1.1 to 4.4
- 34. 8. Hydrogenation of Nonpolar Substrates (Alkynes cis-Alkenes)
- 35. 9. Assymmetric hydrogenation by Chiral FLPs
- 36. 10. Conversion of CO2 to Fuels
- 37. FLP HYDROGENATIONS unprecedented paradigm for H2 activation and use Advantages 1. Avoids cost of precious metal catalysts 2. Avoid cost of separation of toxic metal residues 3. Greener catalysts as uses readily accessible abundant elements Goals 1. Enhance catalyst activity 2. Broaden range of applications 3. Develop selective FLP catalysts
- 38. Hydrogen storage: 0.25 wt% far below 6-9 wt% for practical use Small Molecule Activation
- 39. Questions